Leonardo da Vinci studied a ball bearing using small metal balls to reduce friction.
His late-fifteenth-century sketches show balls arranged between surfaces so that one part could rotate more freely against another. The rolling balls replace much of the sliding friction that would occur if two solid surfaces rubbed directly together.
Leonardo’s design is often cited as an early ball-bearing concept, but it was not a modern sealed bearing. The balls were not necessarily held in a complete cage, and the materials and lubrication available at the time limited durability. Later engineers developed more reliable arrangements for machinery, bicycles, vehicles, and industrial equipment.
The bearing study illustrates Leonardo’s habit of examining friction as a central engineering problem. It also connects with his broader investigations of gears, axles, and rotating machines. Calling him the inventor of every modern bearing overstates the evidence; his importance lies in recording and developing an early workable principle.